Piezoelectric pressure transmitter for an internal combustion engine

ABSTRACT

A cylinder pressure transmitter has means mounting piezoelectric means to provide an electrical signal corresponding to the pressure in a cylinder of an internal combustion engine. A metal diaphragm is arranged to be movable in response to variations in cylinder pressure. Rigid metal motion transfer means and rigid motion transfer means of a material of relatively lower thermal conductivity are arranged in sequence between the diaphragm and the piezoelectric means to accurately transfer movements of the diaphragm to the piezoelectric means while retarding transfer of heat from the cylinder environment to the piezoelectric means through the diaphragm. Preferably the diaphragm is formed of a clad metal laminate.

BACKGROUND OF THE INVENTION

The field of this invention is that of pressure sensors and theinvention relates more particularly to a cylinder pressure transmitterresponsive to variations in pressure within a cylinder of an internalcombustion engine to provide control signals for use in regulatingengine operation.

In commonly assigned, copending patent applications Ser. Nos. 561,842and 561,757 filed Dec. 15, 1983, cylinder pressure transmitters areshown to comprise a body mounting pressure responsive piezoelectricmeans in sealed relation to an engine cylinder to be responsive tovariations in cylinder pressure during engine operation to provideinitial electrical signals representative of pressure variations in thecylinder. Those transmitters include metal diaphragms which shield thepiezoelectric means from the cylinder environments while transmittingpressure forces from the cylinders to the piezoelectric means forgenerating the desired pressure responsive signals. High temperatureelectronic means are carried and electromagnetically shielded on themounting body of the device for amplifying the signals provided by thepiezoelectric means to provide low impedance signals for transmission tocomputer control or other signal processing means at a location remotefrom the engine cylinder for regulating engine operation to improveperformance. However such cylinder pressure transmitters are somewhatdifficult to manufacture at low cost with uniform properties and highreliability and the piezoelectric means tend to be subjected toundesirably high temperatures due to heat-transfer from the enginecylinder environment through the diaphragm. The transmitters are alsosubjected to heavy vibrations during use so that of electricalconnection reliability is of concern. Reference is also made to thecommonly assigned copending applications Ser. Nos. 665,327, 665,340 and665,490 filed of even date herewith.

BRIEF SUMMARY OF THE INVENTION

It is an object of this invention to provide a novel and improvedcylinder pressure transmitter; to provide such a pressure transmitterwhich is adapted to be manufactured with improved economy, uniformityand reliability; and to provide such a pressure transmitter which isbetter adapted to withstand the severe operating temperatures andvibration conditions likely to be encountered in an internal combustionengine environment.

Briefly described, the novel and improved cylinder pressure transmitterof this invention comprises piezoelectric means adapted to provide anelectrical signal in response to application of pressure. Means mountthe piezoelectric means to be responsive to pressures in a cylinder ofan internal combustion engine during normal running operation of theengine for providing electrical signals corresponding to the cylinderpressures. The mounting means include a metal body having a chamberopening at one end of the body and the piezoelectric means areaccommodated in the body chamber. Screw threads or the like are providedon the body near one end of the body for sealing the body end in anengine well communicating with the engine cylinder. Diaphragm means aresecured to the body over the chamber opening, preferably to be flushwith an end wall of the cylinder. The diaphragm means are responsive tovariations in cylinder pressure for transferring pressure forces to thepiezoelectric means to provide initial electrical signals correspondingto the cylinder pressures. The diaphragm means also shield thepiezoelectric means from the high temperature, gaseous engine cylinderenvironment. Electronic means are preferably carried andelectromagnetically shielded on the mounting means to amplify theinitial electrical signals for transmission to a location remote fromthe engine cylinder.

The metal body has a neck portion which is of reduced diameter relativeto the screw threads forming a rim around the chamber opening at the endof the body just ahead of the screw threads. The diaphragm meansincludes a cup-shaped metal member having a side-wall which is fittedaround the reduced-diameter, neck-portion of the body. The side wall iswelded to the body entirely around the reduced diameter body portion forsealing the member to the body while disposing the bottom of thecup-shaped member to extend across the body opening to serve as adiaphragm responsive to cylinder pressure variations. Preferably forcetransmitting means of selected materials, surface areas andcrosssectional configurations are disposed in the body chamber betweenthe diaphragm member and the piezoelectric means and the bottom of thecup-shaped member bears against the force transmitting means to apply aselected preload compressive force to the piezoelectric means, theside-wall of the cup-shaped member being welded to the neck portion ofthe body to maintain the desired preload force. Preferably the diaphragmmember is attached to the body with a precise laser weld. In onepreferred embodiment, the force transmitting means has a surface portionof selected radius at one end engaging a selected area of the center ofthe bottom of the cup-shaped diaphragm member and the compressive forceof that member bearing against that radiused surface provides the memberbottom with a slightly domed or parabolic configuration which isaccurately responsive to engine cylinder pressure variations to transfercorresponding forces to the piezoelectric means.

In one preferred embodiment, the force transmitting means includes oneforce spreading component and another component of material ofrelatively low thermal conductivity. Preferably for example a firstrigid force spreading transfer means of metal has a portion of a reducedcross sectional area and a second rigid force transfer means is of aceramic material or the like of relatively low thermal conductivity. Thetwo force transfer means are arranged in sequence in the body chamberbetween the diaphragm and the piezoelectric means to cooperate intransferring forces from the diaphragm to the piezoelectric means toprovide output signals accurately corresponding to cylinder pressureswhile also retarding transfer of heat from the engine cylinder to thepiezoelectric means through the diaphragm.

In one preferred embodiment, the rigid metal force transfer meanscomprises a spherical metal ball and the low thermal conductivity forcetransfer means has a socket-like surface with a configuration of asegment of a sphere rotatably engaged with the ball to facilitatetransfer of forces applied to the diaphragm from the diaphragm to thepiezoelectric means while providing improved retarding of heat-transferto the piezoelectric means.

In another preferred embodiment, the metal force transfer meanscomprises a metal tube having one end engaged with the diaphragm and thesecond force transfer means comprises a ceramic disc resting on anopposite end of the tube. The tube is substantially limited incrosssectional area for retarding heat transfer while still providingdesired strength and rigidity for force transfer purposes. Preferablysubstantial portions of the force transfer means are spaced from themetal body within the body chamber and the screw thread means arelocated so they tend to transfer heat from the body to the engine todissipate heat from the diaphragm before such heat is transferredthrough the body to the piezoelectric means. In one embodiment,thermally conductive metal means are arranged between the metal tube andthe ceramic disc so that heat which is transferred along the tube isshunted away from the ceramic disc to the mounting body to furtherretard heat-transfer to the piezoelectric means.

In a preferred embodiment, conductor means extend from the piezoelectricmeans to connect to first contact means having a selected location onthe mounting body. Electronic means are then positioned on an insulatingceramic substrate or the like and the substrate is mounted on a separatehousing, preferably on a rigid support in such a housing. Second contactmeans are located on the substrate. The housing and the mounting bodyare provided with locating and guide surfaces which cooperate as thehousing is assembled with the mounting body for automatically bringingthe first and second contact means into a secure electrical engagementwhich is adapted to be reliably maintained even when the pressuretransmitter device is subjected to severe vibrations. Means secure thehousing and mounting body together with the contact means in the desiredassembled relation.

DESCRIPTION OF THE DRAWINGS

Other objects, advantages and details of the novel and improved cylinderpressure transmitter of this invention appear in the following detaileddescription of preferred embodiments of the invention, the detaileddescription referring to the drawings in which:

FIG. 1 is a perspective view of the cylinder pressure transmitter;

FIG. 2 is a section view to enlarged scale along line 2--2 of FIG. 1;

FIG. 3 is a partial section view to greatly enlarged scale similar toFIG. 2 illustrating the diaphragm means of the cylinder pressuretransmitter;

FIG. 4 is a section view similar to FIG. 2 illustrating an alternatepreferred embodiment of the cylinder pressure transmitter;

FIG. 5 is a section view similar to FIG. 2 of an alternate preferredembodiment of the cylinder pressure transmitter;

FIG. 6 is a section view similar to FIG. 2 of another alternatepreferred embodiment of the pressure transmitter;

FIGS. 7-8 are partial section views similar to FIG. 2 illustrating otheralternate preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, 10 in FIGS. 1-3 indicates a novel andimproved cylinder pressure transmitter of this invention which is shownto include a metal body 12 of cold rolled steel or the like preferablyhaving the general size and configuration of a small spark plug. Thebody has a chamber 14 opening at one end 12.1 of the body (see FIG. 2)and sealing means such as screw threads 16 are provided near that end ofthe body for mounting the device 10 in sealed relation within a well 18in an internal combustion engine 20 to face the opening of the chamber14 toward the engine to present it to the pressure environment within apiston cylinder 22 in the engine. Piezoelectric means 24 responsive tothe application of pressure for generating an electrical signal areaccommodated in the body chamber 14 and diaphragm means 26 are arrangedover the chamber opening to be responsive to pressure changes in thecylinder to transmit pressure forces to the piezoelectric means togenerate electrical signals corresponding to the cylinder pressures.Preferably the outer surface of the diaphragm means is generally flushwith the cylinder end wall 22.1 as illustrated in FIG. 2. Electronicmeans 28 are mounted and preferably electromagnetically shielded on themetal mounting body 12 to amplify the initial electrical signalsprovided by the piezoelectric means for transmission to computer controlmeans or the like (not shown) at a location remote from the cylinder.

As shown in FIG. 2, the metal body 12 has a neck portion 30 formed as arim around the opening in the chamber 14. The neck portion is of reduceddiameter relative to the screw thread 16 for easy insertion into theengine well 18 and preferably the neck portion has a radiused edge 30.1(see FIG. 3). Preferably the body 12 has another chamber 32 opening atthe opposite body end and a support section 34 is located between thechambers with a passage 36 extending through the support section.Preferably an exterior body portion 12.2 is hexagonal to meet thestandards established by the Society of Automotive Engineers tofacilitate threaded mounting of the device on the engine.

The piezoelectric means 24 preferably comprises an apertured disc ordonut of a material such as a ceramic lead zirconium titanate or leadmetaniobate or the like having a conventional conductivecharge-collecting coating of silver or the like (not shown) on oppositesides 24.1, 24.2 of the disc. Preferably the disc material has Curietemperature above about 175° C. One side 24.1 of the disc bears againstthe support section 34 and an electrode 38 such as an aperturedstainless steel plate or the like bears against the opposite side 24.2so the electrode and support section electrically engage the respectiveopposite disc sides. A conductor rod or wire 40 is welded, soldered orotherwise connected to the electrode as at 40.1 and typically extendsthrough the disc and plate apertures and the passage 36 toward thechamber 32 as shown in FIG. 2. Alternately the electrode is notapertured and one end of the conductor 40 is resistance welded to theelectrode. Preferably an insulator 42 such as a tube oftetrafluoroethylene or the like suitable for use at the hightemperatures likely to be encountered adjacent an engine cylinder isfitted over the conductor to electrically isolate it from thepiezoelectric disc and from the metal body 12.

The diaphragm means 26 as above described includes a cup-shapeddiaphragm member 44, and force transmitting means such as the forcetransfer means 46 and 48 illustrated in FIG. 2. Preferably one of theforce transfer means comprises a rigid metal force spreading componentwhich has at least a portion of limited crosssectional size or surfacearea disposed at a location between the cup-shaped diaphragm member 44and the piezoelectric means 24 to retard heat transfer through the metalforce transfer means. Preferably another one of the force transfer meanscomprises a component of a material of relatively lower thermalconductivity having a relatively large surface area bearing against thepiezoelectric means to facilitate transfer of pressure force to thepiezoelectric means while further retarding heat transfer.

In the preferred embodiment illustrated in FIGS. 1-3, the cup-shapeddiaphragm member 44 has an original configuration in which a generallycylindrical side-wall 44.1 and a generally planar cup bottom 44.2 areconnected by a portion 44.3 of selected radius. Preferably the diaphragmmember is formed of a springy, stiffly resilient temperature andcorrosion resistant metal material such as the alloy called Inconelwhich has a nominal composition by weight of 80 percent nickel, 14percent chromium and 6 percent iron. Such material is fatigue resistantand capable of withstanding the harsh chemical environment of enginecombustion. Preferably the member has a diameter of about 8 millimeters,a material thickness of about 0.005 to 0.010 inches (0.1 to 0.2millimeters), and preferably about 0.007 inches, and a dehpt of about 3millimeters. The force transfer means 46 comprises a spherical metalball of stainless steel or the like and is preferably of a size to berotatable and axially movable along the longitudinal axis of the chamber14 while tending to be centered in the chamber by the chamber sidewalls. If desired the ball is hollow as indicated at 47. The secondforce transfer means 48 comprises a ceramic material of low thermalconductivity such as a strong, easily shaped and somewhat lubriciouspressed steatite material, or glass or the like. The second forcetransfer means has one side 48.1 which is preferably of relatively largesurface area corresponding generally to that of the piezoelectric disc24 for applying compressive force to the disc across the entire discsurface 24.2. The opposite side 48.2 preferably has a relatively smallersurface area in the shape of a socket or segment of a sphere of adiameter substantially corresponding to that of the ball 46 rotatablyengaged with the ball.

In assembling the structure illustrated in FIG. 2 and 3, the cup-shapedmember 44 is fitted over the neck portion 30 on the mounting body and ispressed with a selected force near the periphery of the member asindicated by arrows 45 in FIG. 3 so that the bottom 44.2 of thediaphragm member bears against the ball 46 and transfers that force tothe socket 48 to apply a desired, predetermined preload compressiveforce to the piezoelectric means. The side wall 44.1 of the cup-shapedmember is then welded as at 50 to the mounting body neck 30 for securingthe cup member in the desired preload position on the mounting body.Where the diaphragm member material is thin relative to the bottommaterial as illustrated in FIG. 3, the weld 50 is preferably formed atthe edge of the rim of the cup-shaped member 44 as shown in FIG. 3 andpreferably comprises a precisely located pulsed laser weld formed aroundthe mounting body neck 30 as diagrammatically illustrated in FIG. 3 bythe arrow 51. With such a weld the cup member is sealed over the chamber14 and retains the force transmitting means with a selected preloadcompressive force while the cup member material retains its initialspring resilience. In that arrangement, the original configuration ofthe diaphragm member as indicated by the broken line 44.4 in FIG. 3 issomewhat altered so the cup bottom 44.2 has a somewhat domed orparabolic shape and so that the cup bottom is adapted to flex in areliable and consistent manner in response to fluid pressure forcesapplied to the diaphragm as indicated by arrows 43 in FIGS. 1 and 3 fortransmitting the presssure forces to the piezoelectric means 24. Theradius 30.1 on the mounting body neck assures that such flexing is freeof interference with the neck.

The screw threads 16 are preferably located on the body 12 at a selecteddistance A from the diaphragm member 44 so that when the device 10 ismounted on the engine 22 by means of the threads, the threads engage theengine immediately adjacent the fluid coolant passages diagrammaticallyillustrated at 53 in FIG. 2 which are typically provided in an internalcombustion engine for dissipating heat from the engine in the area closeto the cylinders 18. The chamber 14 is preferably of selected lengthsuch that the piezoelectric means 24 are located in the chamber at adistance B from the diaphragm member which is equal to, lesser orgreater than the distance A as may be preferred. Where the piezoelectricmeans is located at a distance B equal to or less than the distance Abut adjacent the cooling means 53, the piezoelectric means is locatedwhere heat is being most rapidly dissipated from the mounting body tokeep the piezoelectric means relatively cool either during runningoperation of the engine or during the initial period after shutting offthe engine when external engine temperatures may tend to rise sharplyfor a brief period of time. Alternately, where the distance B is greaterthan the distance A, the piezoelectric means have a greater spacing fromthe engine cylinder thermally isolating the piezoelectric means from thecylinder temperatures as will be understood.

The force transfer means 46 and 48 are arranged to transmit pressurefrom the diaphragm member 44 to the piezoelectric means while furtherretarding heat-transfer from the engine cylinder to the piezoelectricmeans through the diaphragm means. That is, the limited crosssection orsurface area 46.1 of the first force transfer means engages thediaphragm bottom 44.2 at a location between the diaphragm bottom and thepiezoelectric means 24 and accordingly heat transfer to thepiezoelectric means through that limited crosssection or area of theball is substantially retarded. However, the rigid high strengthcharacter of the ball material assures that any pressure force appliedto the diaphragm bottom 44.2 is properly transmitted to the ball. Thesocket surface 48.2 of the second force transfer means engages asimilarly sized but still limited cross-section or surface area of theball at a second location between the diaphragm and piezoelectric meansso that, while the area of that surface engagement assures propertransmission of presssure forces to the ceramic socket member withreduced risk of cracking, heat transfer to the piezoelectric meansthrough the second force transfer means is again retarded. Use of thesocket compensates for any lack of parallelism in the structure so thelarger surface area side 48.2 of the socket reliably applies pressureforce over the entire side 24.2 of the piezoelectric disc. Accordinglythe device 10 provides improved transmission of pressure forces to thepiezoelectric means while also providing improved retardation of heattransfer to the piezoelectric means for improved device reliability andservice life.

In that preferred embodiment of the invention as shown in FIG. 2, theelectronic means 28 preferably comprises high temperature hybridelectronics or the like such as have been described in the earlierfiled, copending patent applications noted above. In this embodimenthowever, the electronics 28 are preferably mounted on an insulatingsubstrate 28.1 of a ceramic material or the like as diagrammaticallyshown in FIG. 2 and the substrate is mounted in a housing means 52 on arigid support such as the cylindrical housing wall 52.1 so that one edge28.2 of the substrate is preferably disposed somewhat spaced from therigid support at a predetermined positive location in the housing 52.The housing means is preferably detachably mounted on the body so thatthe electronic means 28 in the housing are secured in a predeterminedposition relative to the body 12 to be easily and reliablyinterconnected with the piezoelectric means through the conductor 40 andto be retained in that interconnection when subjected to the heavyvibrations likely to be encountered in an internal combustion engineenvironment. Preferably for example, the body chamber 32 provides guidesurfaces 32.1 and a locating surface 32.2. The electronic meanssubstrate 28.1 is disposed closely within the housing means 52 so that acylindrical side wall 52.1 of the housing provides a rigid support foredges 28.3 of the substrate and also provides a guide surface 52.2, thehousing also having locating surfaces 52.3 and 52.4 provided on ahousing flange. Terminals 28.4 provided on the electronic meanspreferably extend from the housing means 52 in any conventional manneras shown in FIG. 2. The electronic means are provided with first fixedcontact means 54 such as a circuit path termination at the edge 28.2 ofthe substrate as diagrammatically illustrated in FIG. 2, that portion ofthe edge 28.2 being spaced from the cylinder 52.1 as will be understood.Second, resilient, electrical contact means 56 are mounted on the body12 connected to the conductor 40 to mate with the substrate contact 54.Preferably for example, a pair of spring leaves 56.1 (only one beingshown) are secured to the conductor 40 by soldering or the like and areinsulated from the body 12 by a bushing 56.2. The guide and locatingsurfaces of the housing means 52 and the device body 12 then cooperateas the housing body is inserted into the body chamber 32 to guide thesubstrate edge with the fixed and resilient contact means 54 between thespring leaves 56 into secure and reliable electrical engagement witheach other. A body flange 12.3 is then rolled or otherwise formed overthe housing locating surfaces for securing the electronic means on thebody in secure and reliable electrical connection to the piezoelectricmeans 24. The metal body 12 surrounds the electronic means 28 in thechamber 32 as shown for providing the electronic means, thepiezoelectric means, and the connection therebetween withelectromagnetic shielding.

In another alternate preferred embodiment of the invention as shown inFIG. 4, wherein corresponding components are identified by correspondingreference numerals, the housing means 52 a is formed of metal and ametal support 53 a for the substrate 28.1 a extends into the bodychamber 32 a. A fixed contact pin 54 a is connected to the circuit pathon the substrate and the resilient second contact means comprises aspring clip 56 a having spring leaves engaging the pin 54 a insertedtherein for precisely locating the end of the substrate 28.1 a to assureprecise engagement between the fixed and resilient contact means 54 aand 56 a as will be understood. Preferably the space within the chamber32 a is filled with a potting material 58 a of any conventional type forthermally and electrically isolating the electronic means from the body12 a while also securing the electronic means against vibration forces.For example a highly viscous material 58 a could be introduced aroundthe electronic means to reduced the effects of vibration.

In another alternate preferred embodiment as shown in FIG. 5, thediaphragm means 26 b comprises a single component force transmittingmeans 60 b in the form of a ceramic member having one side 60.1 bbearing against the piezoelectric means and having an opposite side 60.2b of a radius corresponding to the ball 46 b preferably tapering asindicated at 60.3 b. The force transmitting means is assembled with thecup-shaped member 44 b in the manner previously described and the singleforce transmitting component is centered and is of relatively low massto cooperate with the cup-shaped member to provide precise pressureresponsive characteristics in the device.

In the embodiment shown in FIG. 5 the electronic means 28 b ispreferably mounted on a ceramic substrate 28.1 b which is mounted on thehousing 52 b. Preferably for example, a pin 62 b is soldered to circuitpath means (not shown) on the substrate and the pin is welded orotherwise connected to the terminal 28.4 b as diagrammatically indicatedat 64 b in FIG. 5. The first contact means 54 b are provided on thesubstrate edge by securing a U-shaped spring clip to circuit path means(not shown) on the substrate. The second contact means 56 b comprises anextension of the conductor 40 b as shown in FIG. 5 and the insulator 42b efectively seals the passage 36 b. An epoxy or other fixed holdingcompound curable or settable in situ or the like is deposited in thebottom of the chamber 32 b and the housing 52 b is mounted on the body12 b so the locating surfaces 52.2 b are engaged with the body and sothat the first contact clip 54 b slips over and electrically engages thesecond contact means 56 b. Preferably a barb 54.1 b on one leg of theU-shaped clip extends back on itself to grip the contact means 56 b toprovide an assured connection between the contact means. The epoxy isthen set or cured in situ for locking the contact means 54 b and 56 bsecurely together. The flange 12.3 b then secures the device inassembled relation. Preferably a resilient or viscous potting compound58 b is also used over the fixed holding compound 66 b.

In another alternate embodiment as illustrated in FIG. 6, the passage 36c formed in the mounting body 12 c is preferably tapered from a largeropening at the chamber 32 c to a narrower opening adjacent thepiezoelectric donut 24 c. The first contact means 54 c comprises aspring lead with an insulator 54.1 c which is secured to circuit pathmeans on the electronics substrate 28.1 c so that it extends into thepassage 36 c with a selected bow in the lead as shown and passes throughthe piezoelectric donut 24 c to resiliently and electrically engage theelectrode 38 c. The electrode than serves as the second contact means ofthe device. In that arrangement, the housing 52 c is mounted on the body12 c by means of guide and locating surfaces as previously described andthe tip of the spring lead 54 c is secured in the passage 36 c andguided into resilient electrical engagement with the electrode 38 c aswill be understood. If desired, the electrode 38 c has a small centralopening smaller than the tip of the first contact means 54 c forreceiving and centering the tip in the opening. Preferably the springlead wire 54 c has selected thermal expansion and resilientcharacteristics so the force of the lead engaging the electrode does notsignificantly alter the forces applied to the piezoelectric means duringdevice operation. If desired, a centering support piece 70 c of atemperature resistant polymer such as tetrofluroethylene or the like hasa groove 70.1 c receiving the edge 28.2 c of the electronic substrateand has a tapered locating boss 70.2 c centering the support in thepassage 36 c so the lead 54 c passes through the insulating supportaperture 70.3 c.

In another alternate preferred embodiment of the invention as shown inFIG. 7, the diaphragm means 26 d comprises a cup-shaped diaphragm member44 d corresponding to that previously described with reference to FIGS.1 and 2. In this embodiment however, the first metal force transfermeans 46d preferably comprises a section of stainless steel tube or thelike having one end 46.1 d engaged with the diaphragm bottom 44.2 d. Thesecond force transfer means 48 d comprises a ceramic disc having agroove 48.2 d receiving the opposite end 46.2 d of the tube. The tubehas a relatively small cross-sectional area between the diaphragm andthe piezoelectric means for limiting heat transfer between the diaphragmand piezoelectric means.

In another alternate preferred embodiment as shown in FIG. 8, thediaphragm means comprises a cup-shaped diaphragm member having one end46.1 e of a tube-shaped first force transfer means secured to thediaphragm bottom 44.2 e as indicated at 46.3 e. A thermal shunt member68 e of copper or the like of relatively high thermal conductivity isdisposed between the first force transfer means 46 e and the secondcylindrical ceramic disc force transfer means 48 e to resiliently engagethe metal body 12 e in heat-transfer relation thereto as indicated at68.1 e. Preferably the shunt means is secured to the tube as indicatedat 46.4 e. In that arrangement the tube 46 e and disc 48 e retardheat-transfer from the diaphragm bottom 44.2 e to the piezoelectricmeans and the thermal shunt 68 e tends to further retard such heattransfer by transfering heat away from the opposite 46.2 e of the tubeto the metal body 12 e rather than to transfer such heat to the ceramicdisc 24 e.

In the alternate preferred embodiment illustrated in FIG. 8, thediaphragm member 44 e is formed of a composite metal material havinglayers of metal of selected spring, thermal and corrosion resistantcharacteristics combined for providing improved pressure response andcycle life characteristics in the pressure transmitter. Preferably forexample the diaphragm material has a core layer 44.5 e of stainlesssteel having outer cladding layers 44.6 e of equal thickness of Inconelmetallurgically bonded to opposite sides of the core layer. In such acomposite metal laminate material, the core layer provides the compositewith desired stiff resilience while the clading layers 44.6 e protectthe composite against chemical corrosion in the engine combustionenvironment, the core and cladding layers being selected relative toeach other so that intermetallic compounds or the like are not formedbetween the layers in the high temperature environment such as may tendto cause delamination or embrittlement or the like.

It should be understood that although preferred embodiments of theinvention have been described by way of illustrating the invention, theinvention includes all modifications and equivalents of the disclosedembodiments falling within the scope of the appended claims.

I claim:
 1. A device for providing an electrical signal corresponding to pressure in a cylinder of an internal combustion engine during normal running operation of the engine comprisingpiezoelectric means for providing an electrical signal in response to application of presssure, and means for mounting the piezoelectric means to be responsive to pressure in a cylinder of the engine, the mounting means including a body having a chamber opening at one end of the body accommodating the piezoelectric means therein, means for sealing said one body end in an engine well communicating with the cylinder, and diaphragm means secured over the chamber opening at said one body end to be movable in response to variations in fluid pressure in the engine cylinder to transfer forces to the piezoelectric means to provide an electrical signal corresponding to said cylinder pressure variation while shielding the piezoelectric means from an environment within the cylinder, first rigid motion transfer means of a metal material having a portion of a cross section of relatively lesser area than said diaphragm, and second rigid motion transfer means of a material of relatively lower thermal conductivity then said first motion transfer means, the first and second motion transfer means being arranged in sequence between the metal diaphragm and the piezoelectric means to be freely movable with the diaphragm to transfer movements of the diaphragm to the piezoelectric means to provide said electrical signal while retarding the transfer of heat from the diaphragm through the motion transfer means to the piezoelectric means.
 2. A device according to claim 1 further characterized in that the body is a metal body for transferring heat away from the diaphragm, the sealing means are adapted to secure the body in close heat-transfer relation to said engine for dissipating heat from the body to the engine, and the motion transfer means of relatively low thermal conductivity material is formed of a ceramic material and the metal and ceramic means are mounted in the body chamber with substantial portions of each of the motion transfer means spaced from the body within the chamber for substantially retarding heat-transfer to the piezoelectric means.
 3. A device according to claim 2 further characterized in that a thermally conducting metal shunt is disposed between the metal and ceramic motion transfer means, the shunt being secured in heat-transfer relation to the metal body for shunting heat transferred through the metal transfer means away from the ceramic motion transfer means for further retarding heat-transfer to the piezoelectric means.
 4. A device according to claim 3 wherein said metal motion transfer means comprises a metal tube having one end engaged with said diaphragm and the ceramic transfer means comprises a ceramic cylinder mounted on an opposite end of said tube.
 5. A device according to claim 4 wherein said one tube end is secured to the diaphragm.
 6. A device for providing an electrical signal corresponding to pressure in a cylinder of an internal combustion engine during normal running operation of the engine comprisingpiezoelectric means for providing an electrical signal in response to application of pressure, and means for mounting the piezoelectric means to be responsive to pressure in a cylinder of the engine, the mounting menas including a metal body having a chamber opening at one end of the body accommodating the piezoelectric means therein, having means for mounting the body in an engine well communicating with the cylinder, and having diaphragm means secured over the chamber opening at said one end to be responsive to variations in fluid pressure in the engine cylinder to transfer forces to the piezoelectric means to provide said electrical signals corresponding to said cylinder pressure variations while shielding the piezoelectric means from the gaseous environment in the cylinder, characterized in that the diaphragm comprises a composite metal laminate material having a core layer of a metal material selected for its spring characteristics and an outer layer of another metal material selected for its corrosion resistance characteristics metallurgically bonded to each side of the core layer of the laminate.
 7. A device according to claim 6 wherein the core layer of the laminate material is formed of stainless steel and the outer layers thereof are formed of an alloy having a nominal composition by weight of 80 percent nickel, 14 percent chromiunm, and 6 percent iron. 